1. Field of the Invention
The invention relates to a magnetoresistive (MR) read head and, more particularly, to an orthogonal MR sensor for a read head which has improved sensitivity due to (1) substantial elimination of sense current shunting, and (2) increased control of transverse biasing of the MR stripe.
2. Description of the Related Art
When used herein, the term "MR read head" is intended to refer to a read head that includes a magnetoresistive sensor. An actual read head includes many details of packaging which are necessary for providing a completed commercially usable unit. These details are considered to be known to the skilled artisan.
An MR read head sensor employs an MR thin film layer, hereinafter referred to as an MR stripe, which changes resistance in response to a magnetic field from a moving magnetic medium, such as a rotating magnetic disk. The response of the MR stripe is based on how well the resistance change follows the change in magnetic field flux density. In a typical MR read head the MR stripe is sandwiched between bottom and top insulation gap layers G1 and G2 which, in turn, are sandwiched between bottom and top shield layers S1 and S2. The distance between the shield layers is called the "read gap". The smaller the read gap, the greater the resolution of the MR read head. The MR read head has considerable promise for handling high data rates (1.3 Gb/sec.) required by recent technological advances.
A merged MR head is a combined MR read head and an inductive write head. The merged head is typically mounted on or is part of a slider which has a bottom air bearing surface, hereafter referred to as ABS. When a magnetic disk is rotated with respect to the slider, the slider is supported by an air bearing slightly above (0.075 .mu.m) the rotating magnetic disk.
There are two configurations of an MR read head. In one configuration, a sense current is conducted parallel to the ABS and in the other configuration, the sense current is conducted perpendicular to the ABS, the latter configuration being known as an orthogonal MR read head. The orthogonal read head has several advantages, namely: the amplitude of its readback signal is substantially independent of its track width and the tip of the head at the ABS can be easily grounded to protect the head from electrical shorting. However, the orthogonal read head has several basic problems.
One problem with the orthogonal MR read head is that it has very poor readback sensitivity. In order to accomplish longitudinal biasing, prior art orthogonal MR read heads employ a pair of MR stripes. Each of the MR stripes conducts a sense current which causes them to induce a longitudinal biasing field across one another. This field magnetizes both of the MR stripes into a closed flux state for the purpose of achieving domain noise-free operation. The problem with this arrangement is that the longitudinal biasing is larger than desired and it reduces the permeability of the MR stripes, causing them to be less sensitive to induced signals. A single orthogonal MR stripe could be-stabilized with longitudinal biasing by overlapping antiferromagnetic layers, such as NiMn, FeMn, or NiO, near the lateral edges of the MR stripe. The problem with this arrangement is that the region where the exchange material overlaps the MR stripe will shunt the sense current, thereby degrading sensitivity of the read head. This problem is especially troublesome in orthogonal read heads because the passive exchange-coupled regions are electrically in parallel with the active track whereas in the conventional MR head these regions are electrically in series with the active track.
Another problem is when a merged MR head is employed which is a combination of an orthogonal MR read head and an inductive write head. The merged MR head is constructed using thin film technology. After depositing the thin film layers for the orthogonal MR read head, thin film layers for the inductive write head are laid on top of the MR read head. A problem in the prior art is that the MR read head is non-planar in the area of the track width of the write head. This non-planar condition results from thick conductor leads (typically 1000 to 2000 .ANG.) deposited at top and bottom edges of the MR stripe for providing the sense current and for detecting read voltage. The steps in height created by the conductor leads introduce curvature into the pole tip of the inductive write head. A curved pole tip of a write head will write distorted magnetic bits thereby degrading performance. An attempted solution to this problem is to reduce the thickness of the conductors leads so as to reduce the height of the step created at the top and the bottom of the MR stripe. The problem with this approach is that thinner leads increase the lead resistance which is undesirable for achieving a high sensitivity MR read head.